Glass Ionomer Cements

Question 1

what are the types of glass ionomer cements?

Answer 1

conventional GI and resin modified GI

Question 2

what are the uses of GIC?

Answer 2

restorative, core build up, lining, luting, dressing, fissure sealant, orthodontic cement

Question 3

what are the two components of GIC?

Answer 3

acid (liquid) and base (glass powder)

Question 4

what is the acid used in GIC?

Answer 4

polyacrylic acid, with tartaric acid added to control the setting characteristics of the material

Question 5

which powders are used in GIC?

Answer 5

silica, alumina, calcium fluoride, aluminium fluoride, aluminium phosphate, sodium fluoride

Question 6

what are anyhydrous materials?

Answer 6

the acid is freeze dried and added to the powder, the liquid is distilled water

Question 7

what are encapsulated materials?

Answer 7

consistent powder/liquid ratio

Question 8

what are the 3 phases of the GIC setting reaction?

Answer 8

dissolution, gelation and hardening

Question 9

what happens in dissolution?

Answer 9

acid goes into solution, H+ ions attack the glass surface, Ca, Al, Na and F ions are released which leaves a silica gel around unreacted glass

Question 10

what happens in gelation?

Answer 10

initial set is due to calcium ion crosslinking with the polyacid by chelation with the carboxyl groups (calcium ions are bivalent so they can react with two molecules joining them)

Question 11

what happens in hardening?

Answer 11

trivalent aluminium ions start to crosslink which increases strength, this doesnt start for 30mins and can take a week to complete

Question 12

what happens if GIC is contaminated after the gelation phase

Answer 12

aluminium ions diffuse from material, excessive drying means water will be lost, saliva contamination causes absorption of water, this all leads to a weak material which will be rough and break

Question 13

what can be used to protect conventional GIC after placement?

Answer 13

varnishes, resins (DBA), greases/gels (vaseline)

Question 14

comment on the adhesion of GIC

Answer 14

can bond to enamel and dentine without bonding agent, bond strength not high compared with composite, good sealing ability

Question 15

what is the bonding mechanism of GIC ?

Answer 15

chelation between carboxyl groups in the cement and Ca on the tooth surface, re-precipitation of calcium phosphate (from hydroxyapatite) and calcium salts from the polyacid onto and into the tooth surface, hydrogen bonding or metallic ion bridging to collagen

Question 16

what does a good bond require?

Answer 16

clean surface, conditioned surface

Question 17

what gives materials a better aesthetic presentation?

Answer 17

higher silica content

Question 18

comment on the mechanical properties of GIC?

Answer 18

poor tensile strength, lower compressive strength than composite, poor wear resistance, lower hardness than composite, higher solubility than composite, good thermal properties, no polymerisation contraction, fluoride release, lower modulus, less susceptible to staining and colour change than composite

Question 19

how does GIC release fluoride?

Answer 19

they have an initial fluoride release but then they take up environmental fluoride to release when fluoride content in tooth falls

Question 20

what are the advantages of GIC?

Answer 20

stable chemical bond to enamel and dentine, low microleakage, fluoride release, good thermal properties, no contraction on setting

Question 21

what are the disadvantages of GIC?

Answer 21

brittle, poor wear resistance, moisture susceptible when first placed, poor aesthetics, poor handling characteristics, susceptible to acid attack and drying out over time, problems bonding to composite

Question 22

what powder makes up RMGIC?

Answer 22

fluoro-alumino-silicate glass, barium glass, polyacrylic acid, potassium persulphate, ascorbic acid, pigments,

Question 23

what liquid makes up RMGIC?

Answer 23

HEMA, polyacrylic acid, tartaric acid, water, photoinitiator

Question 24

what is the dual curing method for RMGIC?

Answer 24

acid base reaction, light activated so free radical methacrylate reaction occurs and resin matrix being formed, acid base reaction continues for several hours, REDOX reaction occurs to ensure deeper parts of material is cured

Question 25

what is the tri curing method of RMGIC?

Answer 25

acid base reaction, REDOX reaction begins, light activation and free radial methacrylate reaction, continued REDOX reaction after initial mixing, acid base reaction continues within resin matrix for several hours

Question 26

what are the properties of RMGIC?

Answer 26

good bond to enamel and dentine, superior to conventional GIC, better physical properties, lower solubility, fluoride release, better translucency and aesthetics, better handling

Question 27

what are the disadvantages of RMGIC?

Answer 27

polymerisation contraction, exothermic setting reaction, swelling due to uptake of water, monomer leaching, reduced strength if not light cured, light curing slows acid base reaction, benzoyl peroxides and bromides released which are cytotoxic, fluoride release no better than conventional GIC

Question 28

compare RMGIC to GIC

Answer 28

better aesthetics, easier to use, stronger

Question 29

compare RMGIC to composite resin

Answer 29

easier to use and fluoride release

Question 30

what are the uses of RMGIC

Answer 30

dressing, fissure sealant, endodontic access cavity temporary filling, luting, orthodontic cement, restoration of deciduous and permanent teeth, base or lining